Chromizing over cathodic arc coating
a technology of cathodic arc and coating, applied in the direction of solid-state diffusion coating, superimposed coating process, machines/engines, etc., can solve the problems of significant loss of coating thickness, constant threat to the hardware of such machinery, e.g., turbine blades,
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example 1
to Produce Coating Specimens
[0072]The processes to deposit the various coating specimens in the present application are summarized in Table 1.
[0073]
TABLE 1Definition of the processes to deposit the coatings specimensOperationscathodiccoatingarcdiffusionheavycathodicspecimencoatingDHTpeeningcoatinggrit blastarc coatingDHTpeeningMCrAIY123MCrAIY / 12345diffusedchromidecoatingdiffused1234chromidecoating / MCrAIY(FP)diffused12chromidecoating / MCrAIY(NP)
[0074]A conventional cathodic arc coating MCrAlY is used as a baseline in the hot corrosion and LCF tests.
[0075]The coating specimen MCrAlY / Diffused chromide coating is processed by the conventional method by depositing sequentially a diffusion coating, heavy grip blast to remove the coating surface, and a cathodic arc coating, followed by DHT and peening operation. The MCrAlY / Diffused chromide coating specimen is also used as a baseline in the hot corrosion and LCF tests.
[0076]The coating specimen diffused chromide coating / MCrAlY (FP) and the ...
example 2
of Chromizing Over Cathodic Arc Coating
[0077]FIG. 2 shows optical microscopic views of each coating specimen.
[0078]Nominal coating thicknesses are between about 2.5 mil and 3 mil.
[0079]MCrAlY and MCrAlY / diffused chromide coating specimens are observed to have consistent microstructures as previously predicted.
[0080]In contrast, diffused chromide coating / MCrAlY (FP) and diffused chromide coating / MCrAlY (NP) specimen coatings contain oxides / nitrides inclusions. The majority of these coatings was found to be single phase, likely 7-Ni FCC solid solution, due to Cr enrichment resulting from the diffusion coating deposition. Angular Al-rich phases, like nitrides, resulting from the diffusion coating process, are visible in these coatings as well.
[0081]As shown in the SEM image and associated Cr x-ray map in FIG. 3, the deposition of diffused chromide coating atop MCrAlY on a scrap blade results in the formation of a nearly continuous highly elevated Cr-rich phase at the surface.
example 3
Fatigue (LCF) Test Result
[0082]LCF tests were performed with the coating specimens at the temperature of 1200° F.
[0083]FIG. 4 shows a plot of maximum stress value vs. cycles to failure for each LCF testing. R value for this plot is 0.5.
[0084]Maximum stress value for each specimen was investigated within the range of 120 ksi˜140 ksi. At a maximum stress of 120 ksi, no significant differences were observed between each coating specimen; failure generally occurred at approximately 100,000 cycles. At 140 ksi maximum stress, MCrAlY and MCrAlY / diffused chromide coating specimens failed within the first 100 cycles. diffused chromide coating / MCrAlY (FP) and diffused chromide coating / MCrAlY (NP) specimens failed at greater than 1000 cycles. There is no distinction between the test results of diffused chromide coating / MCrAlY (FP) and diffused chromide coating / MCrAlY (NP).
[0085]In conclusion, there is no indication that LCF resistance is associated with the preparation process, e.g., DHT and p...
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